The present invention relates generally to rivet guns, and more particularly, to a system and method for synchronizing two rivet guns.
Current rivet forming methods include squeeze riveting, electromagnetic riveting, and pneumatic riveting. These riveting methods require considerable worker skill to accurately set rivets and avoid damage to airplane skin.
One of the aforementioned common rivet forming processes is squeeze riveting, which is not an impact forming process. This process uses an actuator (either hydraulic or pneumatic) to slowly apply two opposing (balanced) forces to the rivet. Noise and hand-arm vibration levels are not generated. This process is limited, however, because it requires a rigid steel frame to reach around the part and react against the high rivet compressive forces. For example, the process cannot be used when joining airplane body sections because the necessary gun frame would have to extend around twenty foot long sections.
Another common rivet forming process is electromagnetic riveting (EMR), which delivers a single application of two synchronized opposing impact forces to the rivet. This process generates an impact force by discharging a charged capacitor into a flat faced coil located in a hand held gun. The coil induces eddy currents in an adjacent copper faced mass driver that generates an opposing magnetic force to repel the mass driver into the rivet. Since the mass driver travels over a short distance in a relatively short amount of time, it generates a high reactionary (or recoil) force. For example, the kinetic energy equation is E=0.5 mv2, and the recoil force relationship is F=d(mv)/dt, so for constant energy, the force relationship indicates that a short impact time generates high recoil forces.
One of the only current ways to reduce the EMR recoil force is to add mass to the gun. For instance, an EMR model HH500, from Electroimpact weighs approximately 175 lbs. The EMR guns must be supported from above by a force counterbalance mechanism or supported below by a support platform. These supports make the EMR cumbersome to use, expensive, and they limit useful applications thereof.
Still another common rivet forming process is pneumatic impact riveting. To form a rivet through pneumatic riveting, an impact force is directed to the head of the rivet. The reactionary force is applied by an operator using a bucking bar. Since the operator cannot apply an equivalent opposing force, the impact forces are imbalanced and both structure and bucking bar move in response thereto. The displacement generates motion and initiates structural bending waves that propagate throughout the structure, radiating noise energy. The bucking bar displacement (and motion) results in high acceleration levels. Since multiple impacts are required to form a rivet, these motion effects are multiplied by the impact frequency.
Resultantly, pneumatic impact riveting generates noise ranging from 110 dBA to 130 dBA and generates bucking bar vibration levels in excess of 1000 m/s2. These repeated mechanical shocks are often injurious to the worker, resulting in hearing loss and more serious long-term damage to the circulation and nervous system.
The disadvantages associated with current riveting techniques have made it apparent that a new riveting technique is needed. The new technique should substantially reduce noise and impact vibrations without significantly increasing rivet gun size or weight. The present invention is directed to these ends.
The present invention provides a rivet gun system. The present invention also provides a system for synchronizing two rivet guns.
In accordance with one aspect of the present invention, a rivet gun system, which includes a rivet gun frame having a first end and a second end, is disclosed. A die is coupled to the first end, and a force sensor coupled to the rivet gun frame. The force sensor is adapted to detect a force applied to the die and is further adapted to generate a force signal in response to the force. A holding coil defines a channel within the rivet gun frame. The holding coil is adapted to generate a first electromagnetic force along the channel. The channel includes a first end defined by an end stop and a second end defined by the die. A main coil further defines the channel between the holding coil and the die. The main coil is adapted to generate a second electromagnetic force along the channel. A first plunger is adapted to slide through the channel. A force sensor electronics controller is adapted to receive the force signal and is further adapted to activate the holding coil and the main coil in response to the force signal above a threshold.
In accordance with another aspect of the present invention, a method for riveting including applying a first force to a first side of a compressible object from a first rivet gun and aligning a second rivet gun with the first rivet gun on a second side of the compressible object is disclosed. A second force is applied from the second rivet gun to the second side, and a signal is generated when the first force and the second force are adequate. The first rivet gun is then signaled that the second rivet gun is activated and triggered in response to this signal. The first rivet gun and the second rivet gun are then synchronized and the compressible object is impacted by the rivet gun dies.
An advantage of the present invention is that it includes a verification system to notify rivet gun operators that sufficient pressure has been applied thereto for counteractive force operation. Another advantage of the present invention is the use of optical sensors for synchronization of the two plungers, which ensures that they will impact the rivet at substantially the same time. Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.